Method for inhibiting polymerization of conjugated dienes



United States Patent 3,523,141 METHOD FOR INHIBITING POLYMERIZATION 0F CONJUGATED DIENES Tatsuo Sakashita, Kamakura-shi, Japan, assignor to The Japanese Geon Co., Ltd.

No Drawing. Filed Apr. 18, 1968, Ser. No. 722,190 Claims priority, application Japan, Apr. 26, 1967, 42/26,243 Int. Cl. C07c 7/08, 7/18; B01d 3/34 US. Cl. 260-6665 9 Claims ABSTRACT OF THE DISCLOSURE Inhibitors against polymerization of C -C conjugated dienes in polar solvent solution consist of 0.01- by weight in the solvent of a compound from the group of tert.-mercaptan, alkyl nitrite, thiodipropionitrile, N-nitroso-N-methyl aniline, and a nitro naphthalene. Isoprene in DMF, tested for 24 hours at 155 0., showed excellent results with any of the single substances listed, and some synergism for combinations of two inhibitors in which the second is another of those listed, or a previously known inhibitor.

This invention relates to a method of reducing the tendency of conjugated dienes, e.g., butadiene, isoprene and/ or 1,3-pentadiene, to polymerize in solutions exposed to elevated temperatures.

The term 1,3-pentadiene used herein should be understood to mean both cisand trans-1,3-pentadienes and the term butadiene used herein should be understood to mean 1,3-butadiene.

It is known to use the techniques of solvent absorption and extractive distillation in processes for separating the valuable industrial raw material butadiene in good yield and high purity from a butadiene-containing gas mixture such as the so-called C -hydrocarbon fraction whose chief constituents are, for example, n-butane, isobutane, n-butenes isobutene, butadiene, etc. Further it is well known to use the same techniques in processes for separating isoprene or 1,3-pentadiene in good yield and high purity from isoprene and/ or 1,3-pentadiene containing gas mixture such as the so-called C -hydrocarbon fractions whose chief constituents are, for example, isoprene, 1,3-pentadiene, n-pentane, isopentane, pentene-l, pentene-2, 2- methyl-butene-l, Z-methyl-butene-Z, cyclopentadiene, etc. It is also known that typical solvents used in these processes include dimethyl formamide (DMF), N-methylpyrrolidone, acetonitrile and acetone.

In the operation of these processes, however, the solvent containing the conjugated diene, e.g., butadiene, isoprene or 1,3-pentadiene, is necessarily exposed to elevated temperatures, e.g. from 80 to 150 or even higher, with the consequence that the conjugated diene in the solvent tends to polymerize. As a result, difficulties arise from the clogging of the apparatus with the separating polymer and the formation of a polymeric coating on the inside wall of the apparatus, and continuous operation over an extended period of time becomes practically impossible. At a room temperature or lower, the polymerization of conjugated dienes may be prevented to some extent by addition of a conventionally known polymerization inhibitor, e.g., hydroquinone, 4-ter.-butyl-catechol, p-naphthylamine, Methylene Blue, sodium nitrite, etc. However, the polymerization inhibitors as named above are not satis factory to prevent the polymerization of the conjugated dienes when these dienes are subjected to heat treatment at a relatively high temperature, say, 80-l50 C. or even higher over a long period of time.

An object of the present invention is to provide a 3,523,141 Patented Aug. 4, 1970 method of preventing the polymerization of conjugated dienes in solution at elevated temperatures thereby to overcome the difl'iculties such as hereinabove described during the separation of conjugated dienes from gas mixtures containing conjugated dienes by means of the solvent absorption or extractive distillation process. Other objects of the invention will be obvious from the contents of the specification hereinafter disclosed.

I have found that the corporation of at least one compound selected from aliphatic tertiary mercaptan, 5, 8- thiodipropionitrile, N nitroso N methylaniline, alkyl nitrite, and nitronaphthalene compound into a conjugated diene-containing solution reduces the tendency of the conjugated diene to polymerize. In particular, we have found that little or no polymerization of butadiene, isoprene or 1,3-pentadiene occurs when the solution is exposed to elevated temperatures. Further, the invention enables us to prevent the polymerization of butadiene, isoprene or 1,3-pentadiene even when water is present in a solution containing these conjugated dienes. Accordingly, the present invention provides a method of reducing the tendency of butadiene, isoprene and/or 1,3-pentadiene to polymerize in solutions exposed to elevated temperatures, which comprises adding to the solution, as polymerization inhibitor, at least one of the above-named compounds. The invention also include a butadiene, isoprene or 1,3-pentadiene solution containing, as polymerization inhibitor, at least one of the above-named compounds.

The invention is particularly applicable to butadiene, isoprene or 1,3-pentadiene solution wherein the solvent is a typical solvent used in the separation of butadiene, isoprene or 1,3-pentadiene from butadiene, isoprene or 1,3-pentadiene containing gas mixtures by solvent absorption or extractive distillation as discussed hereinbefore. By means of the invention, it is, therefore, possible to separate butadiene, isoprene or 1,3-pentadiene stably and continuously over an extended period of time from the mixed gases containing butadiene, isoprene or 1,3- pentadiene by means of the solvent absorption or extractive distillation processes, without employing apparatus made from such expensive materials as stainless steels. Although the amount of the polymerization inhibitor compound used is capable of wide variation depending upon such factors as the class of solvent, the water content of the solvent, operating conditions and the presence or absence of iron rust, in general, the objectives of this invention can be achieved by the incorporation of about 0.01-10%, and preferably 0.055%, based on the weight of the solvent. It is, of course, possible to add these compounds in amounts in excess of the foregoing range, as no particular detrimental effects are observed.

Suitable aliphatic tertiary mercaptans can be generically expressed by the chemical formula wherein n is a number of 0-10. Especially preferred as the aliphatic tertiary mercaptan are tertiary butylmercaptan, tertiary lauryl mercaptan, etc. Suitable alkyl nitrite can be expressed by the general formula RONO, wherein R is an alkyl group having 3 to 8 carbon atoms. Typical compounds are, for example, isopropyl nitrite, isoamyl nitrite, octyl nitrite, etc. Nitronaphthalene compounds used herein can be expressed by the general formula wherein X and Y, same or different, are H, OH,

I CH NH or -NO Typical compounds are, for example, a-nitronaphthalene, ,S-nitronaphthalene,1,8-dinitronaphthalene, l-nitro-2-methylnaphthalene, nitro-a-naphthol, 2,4-dinitro 1 naphthol, 4-nitro-l-naphthylamine, 4-nitro-2-aminonaphthol, etc. Other compounds useful as a polymerization inhibitor according to the invention are B,5-thiodipropionitrile, N-nitroso-N-methyl aniline and compounds. Presumably, this is the result of a syner gistic action between these substances and the additive use in accordance with the present invention. Known substances of this class include, for example, Methylene Blue, sodium nitrite, hydroquinone, sulphur, phenolic compounds such as tertiary butyl catechol, and aromatic amines such as ,B-naphthylamine. The conventional amounts or less of such substances may be used.

It is to be noted that the solvent solutions containing butadiene, isoprene and/or 1,3-pentadiene can be equally prevented from polymerization by the incorporation of the polymerization inhibitor according to the present invention. Further, their polymerization inhibiting effect does not decrease at all even in the presence of acetylenes such as methyl acetylene, vinyl acetylene, propyl acetylene, or allenes such as 1,2-butadiene. More specifically, polymer formation can be inhibited by adding the polymerization inhibitor to a solution containing the acetylenes or allenes in addition to butadiene, isoprene and/or 1,3-pentadiene.

The polymerization inhibitors according to the invention are also effective in the presence of saturated hydrocarbons such as butane, n-pentane and isopentane, monoolefins such as butene-l, isobutene, pentene-l, pentene-Z, 2-methylbutene-1, 2-methylbutene-2, and cyclopentadiene. Accordingly, the incorporation of these polymerization inhibitors to the so-called C or C -hydrocarbon fraction is completely effective to undesired polymerization of butadiene or isoprene and 1,3-pentadiene.

Now the present invention will be explained in detail in conjunction with the following examples.

EXAMPLE 1 A glass tube was charged with dimethyl formamide and the various compounds in the amounts hereinafter indicated. Butadiene was introduced to a gauge pressure of 5.5 kg./cm. while maintaining a temperature of 155 C. On examining the state of the solutions 24 hours later. the following results were obtained.

o. (8) 2,4-dinitro-1-naphthol (5,000 p.p.m.)-. Transparent.

EXAMPLE 2 An autoclave having iron rust on its inside wall was charged with dimethyl formamide and the various compounds in the amounts hereinafter indicated. While main taining a temperature of 155 C. in a state in which the mixtures were in contact with the iron rust, butadiene was introduced to a gauge pressure of 6 kg./cm. On examining the state of the solutions 48 hours later, the following results were obtained.

Additive State of Solution (1) None Large amount of polymer separated.

(2) t-Butyhnercaptan (5 vol. percent) Slightly turbid.

(3) t-Laurylmercaptan (5 vol. perccnt). Practically transparent.

(4) B,B-Thiodipropionitrile (5 vol. per- Slightly turbid.

cent). (5) Ngpitroso-N-methylaniline (5 vol. pcr- Practically transparent.

cen (6) Isoamylnit-rite (5 vol. percent) Do. (7) BDii iit ronaplitiialene (5,000 ppm)... Transparent. (8) ZA-dinitro-l-naphthol (5,000 p.p.m.) D (9) 4-nitro-1-naphthylamine (5,000

p.p.m.). (10) 2-rnethyl-Lmtronaphthalene (5,000 Do.

0. Practically transparent.

p.p.m.)

EXAMPLE 3 An autoclave having iron rust present on its inside wall was charged with dimethyl formamide and the various compounds in the amounts hereinafter indicated. Butadiene was introduced to a gauge pressure of 6 kg./cm. while maintaining a temperature of 155 C. The mixtures were in contact with iron rust. On examining the state of the solution 48 hours later, the following results were obtained.

Additive State of Solution (1) None Large amount of polymer separated.

(2) Sodium nitrite (1,000 p.p.m.) Tlll'bld.

(3) Sulphur (500 p.p.rn.)

Polymer separated. (4) Methylene Blue (500 p.p.m.) Do.

percent), sulphur (500 p.p.m.).

(11) Isoamyl nitrite (5 vol. percent), Practically transparent.

naphthylamine (500 p.p.m.).

(12) fi-Dinitronaphthalene (5,000 p.p.m.), Transparent.

4-t-butylcatechol (1,000 p.p.m.)

(13) a-Nitronaphthalene (5,000 p.p.m.), Do.

Sodium nitrite (1,000 p.p.m.).

EXAMPLE 4 The same conditions as given in Example 3 were used to evaluate the joint use of two compounds selected from the polymerization inhibitors of the present invention. The results are set forth below.

Additive State of Solution (1) t-Butylmercaptan (2.5 vol. percent.) 6, Practically transparent.

B-Thiodipropionitrile (2.5 vol. percent).

(2) t-Laurylmercaptan (2.5 vol. percent), Do.

Isoamyl nitrite (2.5 vol. percent).

(3) B,BThiodipropionitrile (2.5 vol. per- Do.

cent), Isoamyl nitrite (2.5 vol. percent).

(4) N-nitro-N-inethylaniline (2.5 vol. per- Do.

cent), B,B-Thiodipropionitrlle (2.5 vol. percent).

(5) 2,4-dinitro-l-naphthol (3,000 p.p.m.), Transparent.

Isoamyl nitrite (2.5 vol percent).

(6) a Nitronaphthalene (3,000 p.p.m.), Do.

t-Butylinercaptan (2.5 vol. percent).

(7) fi-Dinitronaphthalene (3,000 p.p.m.), Do.

N-nitrosoNn1ethylani1ine (2.5 vol. percent).

EXAMPLE 5 An autoclave having iron rust on its inside wall was charged with dimethyl formamide and the various compounds in the amounts hereinafter indicated. While maintaining a temperature of 155 C. in a state in which the mixtures were in contact with the iron rust, isoprene was introduced to a gauge pressure of 3 kg./cm. On examining the state of the solutions 24 hours later, the following results were obtained.

Additive State of Solution Additive State of Solution (1) None Large amount of polymer (1) None Larege amount of polymer separate separated. (2) Sodium nitrite (1,000 .p.m.) Polymer separated. (2) Sodium nitrite (1,000 p.p.m.). Turbid. (3) Sulphur (1,000 p.p.m. Large amount of polymer (3) Sulphur (1,000 p.p.m.) Polymer separated.

separated. (4) Methylene blue (1,000 p.p.m.) o. (4) Methylene blue (1,000 p.p.m.)-. Polymer separated. (5) 4-t-buty1catechol(1,000 p.p.m.) Do. (5) 4-t-butyleatechol (1,000 p.p.m.) Do. (6) t-Butylmercaptan (5 vol. pereent)-.. Transparent (6) t-Butylmercaptan (5 vol. percent) Transparent. (7) B,B-Thi'odipropionitrile (5 vol. per- Do. (7) fi,B-Thiodipropionitrile (5 vol. per- D0. cent, sodium nitrite (1,000 p.p.m.).

cent), sodium nitrite (1,000 p.p.m.). (8) Isoamyl nitrite (5 vol. percent), 4-t- D0. (8) t-Laurylmereaptan (5 vol. percent), Practically transparent. butylcatechol (1,000 p.p.m.).

methylene blue (1,000 p.p.m.). (9) N-hitroso-N-methylaniline (5 vol. per- Do. (9) N-nitroso-N-methyleniline (5 voLper- Transparent. cent cent). (10) B-Dinitronaphthalene (5,000 p.p.m.), Practically transparent. (10) Isoamyl nitrite (5 vol. percent), Slightly turbid. sulphur ,000 p.p.m.

sulphur (1,000 p.p.m.). (11) 2,4-dmitro-1-naphthol (5,000 p.p.m.) Transparent. (1g 2,4-dD in tTit ro-l-iligglghol p.p.m.))- Tranfiparent.

1 5- ini onap ene p.p.m. o.

4-t-butylcatech0l 1,000 p.p.m.). 15 EXAMPLE 9 An autoclave having iron rust on its inside wall was Emma} LE 6 charged with acetonitrile and various additives in the An autoclave having iron rust on its inside wall was amounts hereinafter indicated. While maintaining a temcharged with dimethyl formamide and the various compcrature of 120 C., isoprene was introduced to a gauge pounds in the amounts hereinafter indicated. While main- P s f 7 g-/ 24 hours, the State f t taining a temperature of 155 C, in a state in which the solutions were observed with the following results. mixtures were in contact with the iron rust, 1,3-pentadiene (which consists of 67% by weight of trans-1,3-pentadiene Additive State of Solution and 33% by weight of cis-1,3-pentadiene) was introduced (1) None Large amount of po1ymer to a gauge pressure of 2.5 kg./cm. After 24 hours, the 25 (2) sodiummmte (1000p m) a fi sgstate of the solutions were observed with the following (3) 4 -but 1oatooho1krooo'gi iniir'li ur l l d. p results. (4) t-Butylmercaptan (5 vol. percent) Practically transparent.

(5) B,B-Thiodipropionitr1le (5 vol. per- Slightly turbid. cent), sodium nitrite (1,000 p.p.m.). Additive State or solution Isoamylmtnte p Dobutylcatechol (1,000 p.p.m.). 1 None Large algomt of polymer g gg g y a pa entsepara e (2) Sodium nitrite (1,000 p.p.m.) Polymer separated. flp (5,000 {LP-111')" D0 2 d i ll l gi' 'iih s a t r 1 ..m. .-maounoo er 2 i 44: 1) i l t 1 (1 00: p Lsepargiged. t f l EXAMPLE l0 5 -u caeco ..m. areamouno oymer t t f pseiaraltledi p t An autoclave having iron rust on its inside wall was 6 uy ercap an 5V0 .percen rac ica y ransparen (7) ,B, Thidipropionitme (5 VOL pep slightly tmbm charged wlth dimethyl forrnarmde and various add tives go i t),4-t but i at hoi upoo p.pjmiiz P t. n t t in the amounts hereinafter indicated. While mamtarmng oamy I11 8 V0 PBICBH [8.0 103. ransparen butylcatechol (1,000 mum). Y a temperature of 155 C., the C hydrocarbon fraction 9 N-l)iitrglsol-lN-n(ilet)l(i)glaniline (5 vol. per- Do. consisting of the following compositions was introduced cent ,s p ur p.p.m. 2 (10) fl-Dinitronaphthalene (10,000 p.p.m.) Transparent. 40 to gauge Pressure of 3 i-t-butylcatechol (1,000 p.p.m.). M01 percent (11) 2,4-dmitro-1-nephthol (10,000 p.p.m.)- Practically transparent. nqaentane 24.35 i-Pentane 15.02 EXAMPLE 7 dsoprene 15.08 The autoclave used in the preceding examples was hyl ene-(1) 6.71 charged with dimethyl formamide and various additives in the amounts hereinafter indicated. While maintaining a 'L -P P temperature of 155 C., the hydrocarbon mixture concyclopemadlene sisting of 40% by volume of butadiene, 30% by volume of isoprene and 30% by volume of 1,3-pentadiene (which 'f Y consists of 67 by weight of trans-1,3-pentadiene and C1S'13Pe11tad1ene 33% by weight of cis-1,3-pentadiene) was introduced to y p e a gauge pressure of 4 kg./cm. After 48 hours, the state 'P F'a) of the solutions were observed with the following results. 1,4"Pe11tad1em Z-methylbutene-(l) 1.13 Additive State of solution Cyclopentane Acetylenes (oi-acetylene) 600 p.p.m. (1) None Large amount If polymer 2 s (H mm (1 000 P p t d The mixture were m contact with lIOIl dust. After 48 hours, 2 g gg g ggfi 5% Sep a e the state of the solutions were observed with the follow- 4 Sulphur 1,000 p.p.m.) Do. 0 mg results. (5) t-Butylmercaptan (5 vol. percent) Transparent. (6) B,fl'l;hioddiipropiolittril1(30301. per-) Practically transparent.

cen so umni n e p.p.m. (7) Is??? ritrlite1 ((156631. perce)nt), -t- Slightly turbid. Addmve State of solution 11 y 08 80 0 p.p.m. s Nnitroso-N-methylanili.ne(5vol.per- Transparent. (1) gggg gggg cen (9) B-Dinitronaphthalene (5,000 p.p.m.), Practically transparent. 5 gEP-gfigfiigfifigflfii V2); 33 2 Sparent 4t'bulylcatechol (11000 cent), methylene blue (1,000 p.p.m.). (l0) 2,4-dm1tro-1-naphthol (5,000p.p.m.).- D0 (4) Isoemyl nitrite (5 vol. percent), 4-t- Do.

(a ii i l i t l fi (5 1 P u all t t -l'.\l 050- -me Yall 1118 V0 .por- 1'30 0 runs 918R EXAMPLE 8 cent), sodium nitrite (1,000 p.p.m.). y p (6) 2,4-dinitro-1-naphthol (5,000 p.p.m.) Transparent. An autoclave having IIOIl rust on its inside wall was 70 charged with N-methylpyrrolidone and various additives EXAMPLE 11 in the amounts hereinafter indicated. While maintaining a temperature of 120 C., butadiene was introduced to a An autoclave having 11'011 rust on its inside wall was gauge pressure of 5.5 kg./cm. After 24 hours, the state charged with dimethyl formamide and various additions of the solutions were observed with the following results. in the amounts hereinafter indicated. While maintaining Additive State of solution (1) None Large amount of polymer separated.

(2) t-Butylmercaptan vol. percent) Transparent.

(3) B,fi-thiodipropionitrile (5 vol. percent) Practically transparent. (4) Isoamyl nitrite (5 vol. percent) Slightly turbid. (5) N-nitroso-N-methylaniline (5 vol. Practically transparent.

percent) (6) 2,4-dinitro-1-naphthol (5,000 ppm.) Transparent.

What I claim is:

1. A method of reducing the tendency of a conjugated diene to polymerize in polar solvent solution exposed to elevated temperatures, which comprises adding to the solution, as polymerization inhibitor, a compound selected from the group consisting of aliphatic tertiary mercaptan, 19,6'-thiodipropionitrile, N-nitroso-N-methyl aniline, alkyl nitrite and nitro-naphthalene compound in amount of 0.01 to by weight based on the solvent of the solution.

2. A method according to claim 1, wherein said conjugated diene is butadiene, isoprene, 1,3-pentadiene or the mixture thereof.

3. A method according to claim 1, wherein said conjugated diene is in the form of a C or C -hydrocarbon fraction.

4. A method according to claim 1, wherein said solution comprises a polar solvent selected from dimethyl formamide, N-methyl pyrrolidone, acetonitrile and acetone.

5. A method according to claim 1, wherein said aliphatic tertiary mercaptan is a compound of the general formula wherein n is a number of 0-10.

6. A method according to claim 1, wherein said alkyl nitrite is a compound of the general formula RONO wherein R is a C -a1kyl.

' 7. A method according to claim 1, wherein said nitronaphthalene compound is a compound of the general formula wherein X and Y, same or different, are -H, OH, CH3, -NH2 01' NO2.

8. A method according to claim 1, wherein, in addition to the said polymerization inhibitor, there is also added a known inhibitor for unsaturated compounds.

9. A method according to claim 1, wherein the known inhibitor is sodium nitrate, Methylene Blue, sulphur, tertiary butyl catechol, B-naphthyl amine, furfural, benzaldehyde or aromatic nitro compound.

References Cited UNITED STATES PATENTS 3,388,041 10/1945 Craig 2039 2,730,489 1/ 1956 Lewis 203-9 2,809,155 10/1957 Buchler 203-9 2,900,421 8/1959 Kharasch et a1. 2939 X 3,309,412 3/1967 Sakuragi et a1. 260666.5 3,340,160 9/1967 Waldby 252405 X 3,405,189 10/1968 Sakuragi et al. 260666.5 3,407,240 10/1968 Sakashita et a1. 260666.5

FOREIGN PATENTS 20,281 1968 Japan.

DELBERT E. GANTZ, Primary Examiner K. E. SCHMITKONS, Assistant Examiner US. Cl. X.R. 

